Sodium is a mineral necessary for life, helping to maintain fluid balance and supporting nerve and muscle operation. Excessive consumption, however, can lead to health concerns. Sodium is present in water globally, and its levels are monitored to ensure water remains palatable and safe, particularly for those with specific health conditions. The optimum level is not a single, universally enforced number but a range of advisory limits designed to protect the most susceptible populations.
Sources of Sodium in Drinking Water
Sodium enters the water supply through both natural geological processes and human activities. Naturally, water dissolves sodium from the weathering of rocks and soils as it moves through the earth. In coastal areas, the intrusion of saltwater into freshwater aquifers can dramatically increase sodium concentrations.
Human activities also contribute significant amounts of sodium to the water supply. Runoff from roads treated with salt for de-icing carries sodium into surface water sources and groundwater. Wastewater effluent, industrial discharge, and sewage contamination can also elevate sodium levels.
An often-overlooked source is the water treatment process itself, specifically the use of ion-exchange water softeners. These units replace hardness minerals like calcium and magnesium with sodium ions, which significantly increase the sodium content of the treated water. Sodium-containing chemicals used in municipal treatment plants for disinfection and pH adjustment may also introduce small amounts of the mineral.
Official Guidelines for Sodium Levels
The Environmental Protection Agency (EPA) does not enforce a Maximum Contaminant Level (MCL) for sodium in drinking water. The EPA issues non-enforceable health advisories and aesthetic recommendations to guide public water systems and health officials. The primary guideline focuses on individuals on a severely restricted sodium diet, typically those limiting intake to 500 milligrams per day.
For this vulnerable group, the EPA recommends that sodium concentrations in drinking water not exceed 20 milligrams per liter (mg/L). This advisory aims to ensure that drinking water contributes only a negligible fraction of their overall sodium intake. The World Health Organization (WHO) does not set a health-based guideline value for sodium but suggests an aesthetic limit.
The aesthetic standard focuses on taste. Sodium levels above a certain point can impart a salty or objectionable taste to the water, making it unpalatable for consumers. The EPA suggests that sodium concentrations should remain between 30 and 60 mg/L to avoid adverse effects on taste. The WHO’s aesthetic guideline for sodium is higher, set at 200 mg/L, as taste sensitivity varies widely among individuals.
Health Considerations for Sodium in Water
While the vast majority of sodium intake comes from food, the sodium content in drinking water is a factor for specific health conditions. Drinking water at the advisory level of 20 mg/L typically contributes less than 50 milligrams per day to the total intake, assuming a consumption of two liters.
The main health concern is for individuals with hypertension, or high blood pressure, who are placed on sodium-restricted diets to manage their condition. For these sodium-sensitive individuals, the small, consistent contribution from water could potentially complicate the management of their blood pressure. Studies have shown an association between high sodium levels in drinking water, particularly above 150 mg/L, and increased blood pressure in some populations.
Infants, especially those fed formula mixed with water, also represent a vulnerable population. Since an infant’s kidneys are still developing, they are less efficient at processing excess sodium, and their daily fluid intake relative to body weight is higher than that of an adult. High-sodium water used to prepare formula could lead to an excessive intake for the infant, potentially affecting their health. For both infants and people with severe sodium restrictions, keeping water sodium levels at or below the 20 mg/L advisory is important.
Home Treatment Options for High Sodium Water
Reverse Osmosis (RO) is the most effective technique for sodium removal. An RO system works by forcing water through a semi-permeable membrane that is fine enough to block nearly all dissolved solids, including sodium ions.
A well-maintained RO system can typically remove between 85% and 99% of sodium from the water, making it suitable for those on restricted diets. Distillation is another viable option, which involves boiling the water and collecting the condensed steam, leaving the sodium behind. Both RO and distillation systems are often installed as point-of-use units, treating water only at the kitchen tap for drinking and cooking.
Standard carbon filters, pitcher filters, and most whole-house filtration systems are generally ineffective at removing sodium. Furthermore, a conventional salt-based water softener, which uses an ion exchange process to reduce water hardness, is counterproductive for sodium concerns. These softeners actively increase the sodium content of the water they treat.